One way of compressing AV (Audio Visual) signals with a high degree of efficiency is so-called DV (Digital Video) method. This encoding method is disclosed illustratively in a publication “Specification of Consumer-Use Digital VCRs Using 6.3 mm magnetic tape,” from The HD DIGITAL VCR CONFERENCE. The DV method has been applied primarily to camcorders (camera-integrated video tape recorders) that utilize a video cassette tape.
A DV signal is input and output through an IEEE (Institute of Electrical and Electronic Engineers) 1394 digital interface (called the IEEE 1394 interface hereunder). FIG. 1 shows a typical format of the signal passing through the IEEE 1394 interface.
The IEEE 1394 interface handles the DV signal in blocks of 80 bytes, each block being called a DIF block. A body of 150 DIF blocks makes up one DIF sequence that has a header section, a subcode section, a VAUX section, and an audio and video section. With SD-DVCR (standard TV signal standard compression mode) in effect, one video frame is constituted illustratively by 10 DIF sequences for the 525-60 system subject to the NTSC (National Television System Committee) standard, or by 12 DIF sequences for the 625-50 system subject to the PAL (Phase Alternating Line) standard. With SDL-DVCR (standard TV signal high compression mode) in effect, one video frame is formed by five DIF sequences for the 525-60 system and by six DIF sequences for the 625-50 system.
One DIF block is made up of a three-byte ID (identifier) at its top followed by a 77-byte data portion. The ID includes a DIF block type representing a section type, a sequence number denoting a color sequence, a DIF sequence number, and a DIF block number. The beginning of a DIF sequence is identified by the header section indicated by the DIF block type in the ID of a DIF block. In the DIF block of the header section, high-order three bits in the first byte are “000.”
The DV signal having the above format is fed through the IEEE 1394 interface in the form of isochronous packets. The payload of an isochronous packet carrying the DV signal is called a source packet. One source packet has a fixed size of six DIF blocks (480 bytes).
FIG. 2 illustrates how DIF blocks of the 525-60 system are related to source packets. In a DV stream, all frames have their contents encoded inside and have a fixed bit rate of 120,000 bytes per frame. That means the number of source packets is fixed per video frame. The number of source packets per video frame in SD-DVCR is 250 for the 525-60 system and 300 for the 625-50 system. According to the DV standard, these DIF blocks are recorded onto a tape recording medium 6.35 mm wide.
In recent years, a number of optical disks have been proposed as a disc-type information-recordable medium that is loaded and unloaded into and out of recording/reproducing apparatuses. Each of these recordable optical disks has a mass storage capacity of up to several gigabytes and a high transfer bit rate of tens of Mbps. As such, these discs have been hailed as a promising medium for recording AV (Audio Visual) signals including video signals. In the coming years, a growing demand is expected for DV recording/reproducing apparatuses capable of recording DV signals to one of such optical disks through an IEEE 1394 interface, the signals being retrieved from the tape medium where they have been recorded by camcorder or the like.
As described above, the increasing storage capacity of a recording medium signifies growing numbers of data items (e.g., video and audio data constituting video materials) being recorded on that medium. Given numerous DV video materials recorded on a single disc, the user is required to perform editing operations so that meaningful series of desired pictures may be selected and reproduced.
Where the edited data is to be reproduced (i.e., where some of the scenes dispersed throughout the disc are to be picked up, arranged into a desired sequence, and reproduced), each scene can be reproduced obviously in seamless fashion. That is because the data representing one scene is recorded continuously on the disc. However, editing often involves putting a plurality of scenes one after another, and these scenes may or may not be reproduced seamlessly.
More specifically, an optical pickup movement and/or a disc rotational delay can occur at a connection point between scenes. At that point, the reading of data is interrupted. If the data in a read buffer have been exhausted during the interruption, data decoding is brought to a stop. This can lead to a temporary freeze of displayed pictures, disrupted audio, or other reproduction irregularities.